1. Field of the Invention
The present invention relates to a sheet output device, a sheet processing apparatus, an image forming system, and a sheet output method. More particularly, the invention relates to a sheet output device configured to receive a sheet-like recording medium (hereinafter referred to as a “sheet”) conveyed thereto and send air to the sheet when outputting the sheet while aligning and stacking the sheet, a sheet processing apparatus that includes the sheet output device, an image forming system including the sheet processing apparatus and an image forming apparatus, and a sheet output method to be performed by the sheet output device. Examples of the sheet-like recording medium include a sheet of paper, recording paper, transfer paper, and OHP (overhead projector) sheet. Examples of the image forming apparatus include a copier, a printer, a facsimile, and a digital multifunction peripheral.
2. Description of the Related Art
Conventionally, sheet processing apparatuses that perform various processing, e.g., postprocessing such as alignment, stapling, folding, and bookbinding, on sheets output from an image forming apparatus are widely known and used. Hereinafter, such a sheet processing apparatus that performs postprocessing is referred to as a sheet postprocessing apparatus. In recent years, variety of sheets desired to be processed by this type of sheet postprocessing apparatus has become noticeably wide. In particular, it has become more common to perform printing using a color image forming apparatus on a sheet of coated paper (hereinafter, coated paper”) that produces a visually-superior image for a brochure, a leaflet, or the like. Meanwhile, coated paper generally has the following properties:
1) high surface smoothness;
2) high inter-sheet clinging force; and
3) low stiffness measured using a Clark method.
These properties can make coated paper less favorable in terms of sheet stackability.
There are known techniques that, in view of such sheet stackability, form a layer of air using a fan so that an output sheet is stacked at a proper position. Known examples of such a technique include a technique disclosed in Japanese Laid-open Patent Publication No. 2011-057313. According to this technique, a sheet output device includes an output unit that outputs a sheet, on which an image is formed, in a sheet output direction and a tray unit that sequentially stacks thereon sheets output from the output unit. The sheet output device includes an air blowing mechanism capable of performing a series of operations on each sheet output from the output unit. The series of operations include blowing air onto a back-surface side of the sheet and stopping air blowing immediately before a trailing end of the sheet exits the output unit.
Such an air blowing mechanism as that disclosed in Japanese Laid-open Patent Publication No. 2011-057313 that blows air using, for example, a fan allows preventing buckling in a sheet conveying direction. However, it is difficult to attain favorable stacking reliably because, in a case where the output sheet is thin paper, the air blowing undesirably causes a leading end of the sheet to flutter.
There is a need for a sheet output device capable of preventing fluttering of a leading end of a sheet and achieving favorable alignment accuracy.
It is an object of the present invention to at least partially solve the problems in the conventional technology.